Improved acoustic-electro converting device having semiconductor granules

ABSTRACT

Semiconductor granules for use in acoustic-electro converting devices are made of alloys consisting of from 10 to 95 atomic weight percent of selenium and from 5 to 90 atomic weight percent of tellurium. The alloy may contain from 1 to 80 atomic weight percent of antimony or lead. The granules are packed in a chamber defined between a moving electrode supported by a diaphragm and a fixed electrode of an acoustic-electro converting device.

United States Patent 1191 Takagi et a1.

[ Oct. 29, 1974 1 IMPROVED ACOUSTIC-ELECTRO CONVERTING DEVICE HAVING SEMICONDUCTOR GRANULES [73] Assignee: Nippon Telegraph and Telephone Public Corporation, Tokyo, Japan 22 Filed: Apr. 18,1973

21 Appl. No.: 352,469

Related US. Application Data [62] Division of Ser. No. 210,800, Dec. 22, 1971.

FOREIGN PATENTS OR APPLICATIONS 1,041,536 10/1958 1,129,412 5/1962 Germany 179/190 Primary ExaminerKath1een H. Claffy Assistant Examiner-Thomas L. Kundert Attorney, Agent, or FirmCharles W. Helzer [5 7] ABSTRACT Semiconductor granules for use in acoustic-electro converting devices are made of alloys consisting of from 10 to 95 atomic weight percent of selenium and from 5 to 90 atomic-weight percent of tellurium. The

[52] US. Cl. 179/122, 179/121 R, 179/190 51 1111. C1 H04r 21/00 "F fwm 1 80 8mm: we'ght F 58 Field of Search 179/122 121 R 110 B 0f ammwny lead- The granules are Packed a 179/l23 d chamber defined between a moving electrode supported by a diaphragm and a fixed electrode of an [56] Rferences Cited acoustic-electro converting device.

UNITED STATES PATENTS 9 Claims, 7 Drawing Figures 2,483,317 9/1949 Laurent 179/122 1 1 -3 7 6 "a z-x h spjfi I Germany 179/110 B V PAIENTEllnc-lzs m4 3845251 Sntnaora AG Resistance 06 current m A) IMPROVED ACOUSTIC-'ELECTRO CONVERTING DEVICE HAVING SEMICONDUCTOR GRANULES This is a divisional application of Application Ser. No. 210,800, filed Dec. 22, 197i.

BACKGROUNDOF THE INVENTION cite as the raw material so thatit is difficult to obtain carbon granules of definite quality at a high yield..Further, prior art carbon granules manifest a large hysteresisfor supplied current and soundpressure as well as a large non'-linear distortion so .that their acousticelectro converting operation is not stable.

Among acoustic-electro convertingdevices utilizing semiconductors oth-erfthan carbon granules may be mentioned those utilizing'PN junctions and those utilizing the piezoelectric effect or. the piezoresistance effect of the semiconductor bulkxHowever, the sensitivity of the acousticelectro converting devices utilizing these materials is much lower than that of the devices using carbon granules.

OBJECTS OF THE: INVENTION Accordingly, it is an object of this inventionto provide a novel acoustic-electro converting devices having an extremely small hysteresis for the supply voltage and sound pressure as well as small non-linear distortion.

Another object of this invention 1 is to provide improved acoustic-electro converting deviceswhich can generate a larger output voltagethan prior art carbon granule devices for a comparablysmall supply current and for a definite sound pressure.

Still another object of this invention is to provide improved utilizing semiconductor granules acousticelectro converting devices which have uniform quality, can be manufactured at a high yield andhave smaller vapor adsorptionthan carbongranules and hence are more stable.

A further object of this invention is to provide novel acoustic-electro converting devices capable of producing a large output for a given value of supply direct current and sound pressure appliedthereto.

Still further object of this inventionis to provide uti-- essentially of from to 95atomic weight'percent of selenium and from 5 to 90 atomic weight percent of tellurium. Further, the alloys may contain from I to atomic weight percent of antimony or lead. In a typical application the semiconductor granules of this invention are packed between a moving electrode supported bya diaphragm and a fixed electrode of the acousticelectro converting device.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a sectional view of an acoustic-electro converting device using the novel semiconductor granules;

FIG. 2 is agraph showing the direct currentoutput voltage characteristics of the novel semiconductor granules;

FIG. 3 is a graph showing the direct currentiresistance characteristics of the novel semiconductor granules;

FIGS. 4A, 4B and 4C show the relationship between the composition of the alloy and AC outputvoltage. AC resistance and available power respectively; and

FIG. '5 is a plot showing the attenuation characteristics of the second harmonic of the audio frequency of the acoustic-electro converting devices utilizing the semiconductor granules embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An acoustic-electro converting device using the semiconductor granules of this invention comprises a cone-shaped duralumin diaphragm *1 having an outer periphery mounted on the inside of the outer wall 3 of an aluminum casing 2. The diaphragm I is provided with a central opening 4 which is covered by a semispherical hollow moving electrode 5. An annular sheet 7 of silk is provided between the inner wall 6 of the casing 2 and the moving electrode 5. A semispherical hollow fixedelectrode 9 is secured concentric with the moving electrodes by an annular insulation washer 8 located below sheet 7. The stationary electrode 9 is clamped between annular insulation washers 8 and 10. Accordingly, a chamberill is defined by silk sheet 7, moving electrode 5, insulation washer 8 and fixed elec- -trode 9. :T he chamber 11' has a volume of about 0.45

cc, for example, and is packed with the semiconductor granules to be described later.

Although the theory of operation of the mechanism of theacoustic-electro converting device shown in FIG.

'1 is not yet fully understood, the following phenomena were noted. When a sound pressure is applied to diaphragm I while a dc voltage is supplied between movexample, of99.999 percent. The components are weighed at a predetermined ratio and the mixture of the components is packed in a glass ampoule with one end closed. After evacuating the ampoule to a vacuum of about l Torr, the open end of the ampoule is sealed. Then, the sealed ampoule is placed in an electric furnace to heat the mixture of the components to a temperature substantially higher than the melting point of the mixture. When the melting point of the raw material is higher than 500C, a quartz ampoule is substituted for the glass ampoule. The ampoule is vibrated in the electric furnace to agitate and admix the molten metal. Thereafter, the ampoule is cooled to room temperature at a rate of about lC per minute thus producing the desired alloy crystals. The crystals are then pulverized to form granules having a particle size of from 0.1 to 0.4 mm.

One example of the characteristics of granules of selenium-tellurium alloy is as follows. In one case, 1.7 g of granules having a grain size of 60 to 100 mesh of a selenium-tellurium alloy containing these elements at an atomic weight ratio of l 9 (Se 1 Te 9) was packed in chamber 11 whereas in the other case 1.4 g of the granules having a grain size of 60 to 100 mesh of a selenium-tellurium alloy containing these elements at an atomic weight ratio of 4 6 (Se 4 Te 6) was packed in chamber 11. The acoustic-electro characteristics of these alloys were measured and the results are shown in the following Tables. The measurements were carried out by supplying a dc current across electrodes and 9 and by applying a sound pressure of about 1 microbar to the diaphragm at a frequency of 1 kH TABLE 1 AC output voltage (mV) FIG. 2

Supplied Current (mA) 2 5 I0 50 Se :Te 9 5 7.8 9.5 '-).I 5.8 Sc-I1Te6 l7 II Ill 14 7 TABLE 2 AC resistance (ohm) FIG.

Supplied Current (mA) 2 S III 20 50 Se 1 :Te I 200 I75 I50 I10 64 Se 4 I l e ti 5000 3200 2100 I300 700 The following example illustrates alloys of selenium-telIurium-antimony. In one case, l.3 g of the granules having a particle size of 60 to 100 mesh of a selenium-tellurium-antimony containing these elements at an atomic weight ratio of I 3 6 (Se l Te 3-Sb 6) was packed in chamber 11 whereas in the other case 1.4 g of the granules of the particle size of 60 to I00 mesh of a selenium-tellurium-antimony alloy containing these elements at an atomic weight ratio of 4 l 5 (Se 4-Te l-Sb 5) was packed in chamber 11. The measured values of the acoustic-electro characteristics of these alloys under the same measuring conditions as in the preceding example are shown in Tables 3 and 4 below.

TABLE 3 AC output voltage (mV) FIG. 2

V 4 TABLE 4 AC resistance (ohm) FIG. 3

Supplied Current (mA) 2 5 I0 20 50 Se l-Te .l-Sb 6 9t) 90 89 78 Se 4-Te l-Sh 5 3100 2100 1420 950 460 These Tables (1-4) show typical data obtained and these data are plotted in FIGS. 2 and 3. FIG. 2 shows a plot of DC current-AC output voltage characteristics. As can be noted from FIG. 2, with the exception of the alloy Se l-Te 3-Sb 6, the novel semiconductor granules show a larger AC output voltage for a small DC current when compared with the well known carbon granules. As shown in FIG. 3 which illustrates the AC resistance characteristics of the novel semiconductor granules, these granules manifest a larger AC resistance than do carbon granules.

From the results of a number of measurements made on granules of alloys of compositions differing in proportions from those described above, it has been possible to make a clear analysis of the acoustic-electro converting characteristics of the semiconductor granules of the selenium-tellurium-antimony system. The results of this analysis are shown by the diagrams in FIGS. 4A, 4B and 4C. FIG. 4A shows the composition dependency of the AC output voltage where a DC current of 5 m A was supplied between the moving electrode 5 and the fixed electrodes 9 when a sound pressure of about I microbar at a frequency of l kH was applied to the diaphragm. FIG. 4B shows the composition dependency of the AC resistance by illustrating the AC resistance between the electrodes at a frequency of l kH whereas FIG. 4C shows the composition dependency of the output power at a DC current of 5 m A.

The hysteresis of the novel semiconductor granules for DC current and sound pressure is much smaller than that of conventional carbon granules. Thus, the operation of the semiconductor granules is extremely stable. Moreover, the distortion in the output voltage with respect to the waveform of the input sound pressure of the acoustic-electro converting device utilizing the semiconductor granules of this invention is smaller than that of the carbon transmitter. Especially, the attenuation characteristic of the second harmonic of the input sound wave is excellent. FIG. 5 shows the attenuation characteristics of the second harmonic output with reference to the fundamental frequency output of the acoustic-electro converting devices using the novel semiconductor granules and carbon granules, respectively.

While the invention has been described in tei ms of selenium-tellurium alloys and selenium-telluriumantimony alloys, it was found that lead could be substituted for antimony with equal satisfactory results. For example, when 2 atomic weight percent of lead was incorporated in a 49 49 seIenium-tellurium alloy, the output voltage was increased 10 percent whereas the AC resistance was decreased 20 percent when compared with selenium-tellurium alloys.

As described above, alloys containing higher percentages of selenium have higher output voltages. Especially under a low supplied current of less than m A, larger output voltages are obtained than with carbon granules. As pointed out above, the electrical resistance increases with the selenium concentration. It has been found that it is possible to adjust the electrical resistance of the novel alloy semiconductor granules by incorporating a halogen into the selenium-tellurium type alloy. For example, when 0.05 percent by weight, of chlorine is added to an alloy containing selenium and tellurium at an atomic weight ratio of 3 7, the output voltage scarecely varied while the AC resistance decreased about percent. The quantity of incorporation of the chlorine may be very small, 0.001 to 0.1 percent being preferred for chlorine.

We claim:

1. An acoustic-electro converting device comprising a diaphragm, a moving electrode secured to said diaphragm, a fixed electrode spaced from said moving electrode and defining a chamber between said moving and fixed electrodes, semi-conductor granules packed in said chamber. said semiconductor granules being made of an alloy consisting of from 10 to 95 atomic weight percent of selenium and from 5 to 90 atomic weight percent of tellurium and granulated into granules having diameters of the order of from 0.1 to 0.4 mm, the semiconductor granule packed chamber defined by said spaced-apart moving and fixed electrodes having a configuration and size such that it exhibits an alternating current resistance ranging in value from 90 ohms to 3.2 kiloohms upon energization with a small DC current of the order of 5 milliamperes supplied across the spaced-apart electrodes.

2. An acoustic-electro converting device according to claim 1 further including an outer supporting casing for movably supporting said moving electrode and fixed supporting means formed on said casing for fixedly supporting said fixed electrode in spaced-apart relationship with respect to said moving electrode to define said chamber for receiving the semiconductor granules.

3. An acoustic-electro converting device according to claim 2, wherein said outer casing is cylindricallyshaped, said moving electrode comprises a conicallyshaped vibrating diaphragm having a quasi-sphericallyshaped electrically conductive hub portion, and said fixed electrode comprises a complimentary quasispherically-shaped conductive electrode member centrally secured within said casing in spaced apart relationship with said hub portion by said supporting means.

4. An acoustic-electro converting device according to claim 3, wherein said fixed quasi-spherically-shaped electrode member includes an outer surrounding annular flange portion secured to a complimentary centrally disposed internal mounting flange centrally formed within said cylindrically-shaped outer casing by suitable annular electrically insulating mounting washers.

5. An acoustic-electro converting device according to claim 4, further including an annular silk screen sheet covering the semiconductor granules packed within the chamber defined by said quasi-spherical fixed electrode and the spaced apart quasi-sphericallyshaped central hub portion of the conically shaped vibrating diaphragm.

6. An acoustic-electro converting device according to claim 5, wherein said alloy further contains from 1 to atomic weight percent of antimony.

7. The acoustic-electro converting device according to claim 5, wherein said allow further contains from I to 80 atomic weight of lead.

8. The acoustic-electro converting device according to claim 1, wherein said alloy further contains from I to 80 atomic weight percent of antimony.

9. The acoustic-electro converting device according to claim 1, wherein said alloy further contains from I to 80 atomic weight percent of lead. 

1. AN ACOUTIC-ELECTRO CONVERTING DEVICE COMPRISING A DIAPHRAGM, A MOVING ELECTRODE SECURED TO SAID DIAPHRAGM, A FIXED ELECTRODE SPACED FROM SAID MOVING ELECTRODE AND DEFINING A CHAMBER BETWEEN SAID MOVING AND FIXED ELECTRODES, SEMI-CONDUCTOR GRANULES PACKED IN SAID CHAMBER, SAID SEMICONDUCTOR GRANULES BEING MADE OF AN ALLOY CONSISTING OF FROM 10 TO 95 ATOMIC WEIGHT PERCENT OF SELENIUM AND FROM 5 TO 90 ATOMIC WEIGHT PERCENT OF TELLURIUM AND GRANULATED INTO GRANULES HAVING DIAMETERS OF THE ORDER OF FROM 0.1 TO 0.4 MM, THE SEMICONDUCTOR GRANULE PACKED CHAMBER DEFINED BY SAID SPACED-APART MOVING AND FIXED ELECTRODES HAVING A CONFIGURATION AND SIZE SUCH THAT IT EXHIBITS AND ALTERNATING CURRENT RESISTANCE RANGING IN VALUE FROM 90 OHMS TO 3.2 KILOOHMS UPON ENERGIZATION WITH A SMALL DC CURRENT OF THE ORDER OF 5 MILLIAMPERES SUPPLIED ACROS THE SPACED-APART ELECTRODES.
 2. An acoustic-electro converting device according to claim 1 further including an outer supporting casing for movably supporting said moving electrode and fixed supporting means formed on said casing for fixedly supporting said fixed electrode in spaced-apart relationship with respect to said moving electrode to define said chamber for receiving the semiconductor granules.
 3. An acoustic-electro converting device according to claim 2, wherein said outer casing is cylindrically-shaped, said moving electrode comprises a conically-shaped vibrating diaphragm having a quasi-spherically-shaped electrically conductive hub portion, and said fixed electrode comprises a complimentary quasi-spherically-shaped conductive electrode member centrally secured within said casing in spaced apart relationship with said hub portion by said supporting means.
 4. An acoustic-electro converting device according to claim 3, wherein said fixed quasi-spherically-shaped electrode member includes an outer surrounding annular flange portion secured to a complimentary centrally disposed internal mounting flange centrally formed within said cylindrically-shaped outer casing by suitable annular electrically insulating mounting washers.
 5. An acoustic-electro converting device according to claim 4, further including an annular silk screen sheet covering the semiconductor granules packed within the chamber defined by said quasi-spherical fixed electrode and the spaced apart quasi-spherically-shaped central hub portion of the conically shaped vibrating diaphragm.
 6. An acoustic-electro converting device according to claim 5, wherein said alloy further contains from 1 to 80 atomic weight percent of antimony.
 7. The acoustic-electro converting device according to claim 5, wherein said allow further contains from 1 to 80 atomic weight % of lead.
 8. The acoustic-electro converting device according to claim 1, wherein said alloy further contains from 1 to 80 atomic weight percent of antimony.
 9. The acoustic-electro converting device according to claim 1, wherein said alloy further contains from 1 to 80 atomic weight percent of lead. 